BackupUtils：

package net.micode.notes.tool;
 
public class BackupUtils {
    private static final String TAG = "BackupUtils";    
    // Singleton stuff
    private static BackupUtils sInstance;   //类里面定义自己类的对象
 
    public static synchronized BackupUtils getInstance(Context context) {
    //当某个线程运行时，要检查其他线程是否也在进行
        if (sInstance == null) {
            sInstance = new BackupUtils(context);
        }
        return sInstance;
    }
 
    /**
     * Following states are signs to represents backup or restore
     * status
     */
    // Currently, the sdcard is not mounted 手机内没有SD卡
    public static final int STATE_SD_CARD_UNMOUONTED           = 0;  
    // The backup file not exist  没有备份文件夹
    public static final int STATE_BACKUP_FILE_NOT_EXIST        = 1;
    // The data is not well formated, may be changed by other programs  数据已被破坏，也可能被修改
    public static final int STATE_DATA_DESTROIED               = 2;
    // Some run-time exception which causes restore or backup fails  超时异常
    public static final int STATE_SYSTEM_ERROR                 = 3;
    // Backup or restore success  成功存储
    public static final int STATE_SUCCESS                      = 4;
 
    private TextExport mTextExport;
 
    private BackupUtils(Context context) {  //初始化函数
        mTextExport = new TextExport(context);
    }
 
    private static boolean externalStorageAvailable() {   //外部存储功能是否正常
        return Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState());
    }
 
    public int exportToText() {
        return mTextExport.exportToText();
    }
 
    public String getExportedTextFileName() {
        return mTextExport.mFileName;
    }
 
    public String getExportedTextFileDir() {
        return mTextExport.mFileDirectory;
    }
 
    private static class TextExport {
        private static final String[] NOTE_PROJECTION = {
                NoteColumns.ID,
                NoteColumns.MODIFIED_DATE,
                NoteColumns.SNIPPET,
                NoteColumns.TYPE
        };
 
        private static final int NOTE_COLUMN_ID = 0;
 
        private static final int NOTE_COLUMN_MODIFIED_DATE = 1;
 
        private static final int NOTE_COLUMN_SNIPPET = 2;
 
        private static final String[] DATA_PROJECTION = {
                DataColumns.CONTENT,
                DataColumns.MIME_TYPE,
                DataColumns.DATA1,
                DataColumns.DATA2,
                DataColumns.DATA3,
                DataColumns.DATA4,
        };
 
        private static final int DATA_COLUMN_CONTENT = 0;
 
        private static final int DATA_COLUMN_MIME_TYPE = 1;
 
        private static final int DATA_COLUMN_CALL_DATE = 2;
 
        private static final int DATA_COLUMN_PHONE_NUMBER = 4;
 
        private final String [] TEXT_FORMAT;
        private static final int FORMAT_FOLDER_NAME          = 0;
        private static final int FORMAT_NOTE_DATE            = 1;
        private static final int FORMAT_NOTE_CONTENT         = 2;
 
        private Context mContext;
        private String mFileName;
        private String mFileDirectory;
 
        public TextExport(Context context) {
            TEXT_FORMAT = context.getResources().getStringArray(R.array.format_for_exported_note);
            mContext = context;
            mFileName = "";    
            mFileDirectory = "";
        }
 
        private String getFormat(int id) {  //获取文本的组成部分
            return TEXT_FORMAT[id];
        }
 
        /**
         * Export the folder identified by folder id to text
         */
        private void exportFolderToText(String folderId, PrintStream ps) {   
            // Query notes belong to this folder  通过查询parent id来制定ID文件夹下的Note
            Cursor notesCursor = mContext.getContentResolver().query(Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION, NoteColumns.PARENT_ID + "=?", new String[] {
                        folderId
                    }, null);
 
            if (notesCursor != null) {                             
                if (notesCursor.moveToFirst()) {
                    do {
                        // Print note's last modified date   ps里面保存有这份note的日期
                        ps.println(String.format(getFormat(FORMAT_NOTE_DATE), DateFormat.format(
                                mContext.getString(R.string.format_datetime_mdhm),
                                notesCursor.getLong(NOTE_COLUMN_MODIFIED_DATE))));
                        // Query data belong to this note
                        String noteId = notesCursor.getString(NOTE_COLUMN_ID);
                        exportNoteToText(noteId, ps);  //将文件导出到text
                    } while (notesCursor.moveToNext());
                }
                notesCursor.close();
            }
        }
 
        /**
         * Export note identified by id to a print stream
         */
        private void exportNoteToText(String noteId, PrintStream ps) {  
            Cursor dataCursor = mContext.getContentResolver().query(Notes.CONTENT_DATA_URI,
                    DATA_PROJECTION, DataColumns.NOTE_ID + "=?", new String[] {
                        noteId
                    }, null);
 
            if (dataCursor != null) { //利用光标来扫描内容，看是callnote或者note二者中的哪一个，靠ps.printline输出
                if (dataCursor.moveToFirst()) {
                    do {
                        String mimeType = dataCursor.getString(DATA_COLUMN_MIME_TYPE);
                        if (DataConstants.CALL_NOTE.equals(mimeType)) {
                            // Print phone number 输出电话号
                            String phoneNumber = dataCursor.getString(DATA_COLUMN_PHONE_NUMBER);
                            long callDate = dataCursor.getLong(DATA_COLUMN_CALL_DATE);
                            String location = dataCursor.getString(DATA_COLUMN_CONTENT);
 
                            if (!TextUtils.isEmpty(phoneNumber)) {  //判断是否为空字符
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        phoneNumber));
                            }
                            // Print call date
                            ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT), DateFormat
                                    .format(mContext.getString(R.string.format_datetime_mdhm),
                                            callDate)));
                            // Print call attachment location 打印调用附件位置
                            if (!TextUtils.isEmpty(location)) {
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        location));
                            }
                        } else if (DataConstants.NOTE.equals(mimeType)) {
                            String content = dataCursor.getString(DATA_COLUMN_CONTENT);
                            if (!TextUtils.isEmpty(content)) {
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        content));
                            }
                        }
                    } while (dataCursor.moveToNext());
                }
                dataCursor.close();
            }
            // print a line separator between note 在注释间打印分隔符
            try {
                ps.write(new byte[] {
                        Character.LINE_SEPARATOR, Character.LETTER_NUMBER
                });
            } catch (IOException e) {
                Log.e(TAG, e.toString());
            }
        }
 
        /**
         * Note will be exported as text which is user readable
         */
        public int exportToText() {    //总函数，调用上面的exportFolder和exportNote
            if (!externalStorageAvailable()) {
                Log.d(TAG, "Media was not mounted");
                return STATE_SD_CARD_UNMOUONTED;
            }
 
            PrintStream ps = getExportToTextPrintStream();
            if (ps == null) {
                Log.e(TAG, "get print stream error");
                return STATE_SYSTEM_ERROR;
            }
            // First export folder and its notes   导出文件夹里面包含的便签
            Cursor folderCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION,
                    "(" + NoteColumns.TYPE + "=" + Notes.TYPE_FOLDER + " AND "
                            + NoteColumns.PARENT_ID + "<>" + Notes.ID_TRASH_FOLER + ") OR "
                            + NoteColumns.ID + "=" + Notes.ID_CALL_RECORD_FOLDER, null, null);
 
            if (folderCursor != null) {
                if (folderCursor.moveToFirst()) {
                    do {
                        // Print folder's name
                        String folderName = "";
                        if(folderCursor.getLong(NOTE_COLUMN_ID) == Notes.ID_CALL_RECORD_FOLDER) {
                            folderName = mContext.getString(R.string.call_record_folder_name);
                        } else {
                            folderName = folderCursor.getString(NOTE_COLUMN_SNIPPET);
                        }
                        if (!TextUtils.isEmpty(folderName)) {
                            ps.println(String.format(getFormat(FORMAT_FOLDER_NAME), folderName));
                        }
                        String folderId = folderCursor.getString(NOTE_COLUMN_ID);
                        exportFolderToText(folderId, ps);
                    } while (folderCursor.moveToNext());
                }
                folderCursor.close();
            }
 
            // Export notes in root's folder   将根目录里的便签导出
            Cursor noteCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION,
                    NoteColumns.TYPE + "=" + +Notes.TYPE_NOTE + " AND " + NoteColumns.PARENT_ID
                            + "=0", null, null);
 
            if (noteCursor != null) {
                if (noteCursor.moveToFirst()) {
                    do {
                        ps.println(String.format(getFormat(FORMAT_NOTE_DATE), DateFormat.format(
                                mContext.getString(R.string.format_datetime_mdhm),
                                noteCursor.getLong(NOTE_COLUMN_MODIFIED_DATE))));
                        // Query data belong to this note 查询数据属于此备注
                        String noteId = noteCursor.getString(NOTE_COLUMN_ID);
                        exportNoteToText(noteId, ps);
                    } while (noteCursor.moveToNext());
                }
                noteCursor.close();
            }
            ps.close();
 
            return STATE_SUCCESS;
        }
 
        /**
         * Get a print stream pointed to the file {@generateExportedTextFile}
         */
        private PrintStream getExportToTextPrintStream() {                  
            File file = generateFileMountedOnSDcard(mContext, R.string.file_path,
                    R.string.file_name_txt_format);
            if (file == null) {
                Log.e(TAG, "create file to exported failed");
                return null;
            }
            mFileName = file.getName();
            mFileDirectory = mContext.getString(R.string.file_path);
            PrintStream ps = null;
            try {
                FileOutputStream fos = new FileOutputStream(file);
                ps = new PrintStream(fos);    //将ps输出流输出到特定的文件
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                return null;
            } catch (NullPointerException e) {
                e.printStackTrace();
                return null;
            }
            return ps;
        }
    }
 
    /**
     * Generate the text file to store imported data
     */
    private static File generateFileMountedOnSDcard(Context context, int filePathResId, int fileNameFormatResId) {
        StringBuilder sb = new StringBuilder();
        sb.append(Environment.getExternalStorageDirectory());  //SD卡的存储路径
        sb.append(context.getString(filePathResId));    //文件的存储路径
        File filedir = new File(sb.toString());        //filedir应该就是用来存储路径信息
        sb.append(context.getString(
                fileNameFormatResId,
                DateFormat.format(context.getString(R.string.format_date_ymd),
                        System.currentTimeMillis())));
        File file = new File(sb.toString());
 
        try {   //如果这些文件不存在，则新建
            if (!filedir.exists()) {
                filedir.mkdir();
            }
            if (!file.exists()) {
                file.createNewFile();
            }
            return file;
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
// try catch 异常处理
        return null;
    }
}